(function flexible(window, document) {
	const docEl = document.documentElement;
	const dpr = window.devicePixelRatio || 1;

	// adjust body font size
	function setBodyFontSize() {
		if (document.body) {
			document.body.style.fontSize = (12 * dpr) + "px";
		} else {
			document.addEventListener("DOMContentLoaded", setBodyFontSize);
		}
	}

	setBodyFontSize();

	// set 1rem = viewWidth / 100
	function setRemUnit() {
		const rem = docEl.clientWidth / 100;
		docEl.style.fontSize = rem + "px";
	}

	setRemUnit();

	// reset rem unit on page resize
	window.addEventListener("resize", setRemUnit);
	window.addEventListener("pageshow", function (e) {
		if (e.persisted) {
			setRemUnit();
		}
	});

	// detect 0.5px supports
	if (dpr >= 2) {
		const fakeBody = document.createElement("body");
		const testElement = document.createElement("div");
		testElement.style.border = ".5px solid transparent";
		fakeBody.appendChild(testElement);
		docEl.appendChild(fakeBody);
		if (testElement.offsetHeight === 1) {
			docEl.classList.add("hairlines");
		}
		docEl.removeChild(fakeBody);
	}
}(window, document));
